Genetic transformation of Rhodopseudomonas sphaeroides by plasmid DNA

Expression of Alternative Nitrogenases in Rhodopseudomonas palustris Is Enhanced Using an Optimized Genetic Toolset for Rapid, Markerless Modifications

The phototrophic bacterium Rhodopseudomonas palustris is emerging as a promising biotechnological chassis organism, due to its resilience to a range of harsh conditions, a wide metabolic repertoire, and the ability to quickly regenerate ATP using light. However, realization of this promise is impeded by a lack of efficient, rapid methods for genetic modification. Here, we present optimized tools for generating chromosomal insertions and deletions employing electroporation as a means of transformation. Generation of markerless strains can be completed in 12 days, approximately half the time for previous conjugation-based methods. This system was used for overexpression of alternative nitrogenase isozymes with the aim of improving biohydrogen productivity. Insertion of the pucBa promoter upstream of vnf and anf nitrogenase operons drove robust overexpression up to 4000-fold higher than wild-type. Transcript quantification was facilitated by an optimized high-quality RNA extraction protocol employing lysis using detergent and heat. Overexpression resulted in increased nitrogenase protein levels, extending to superior hydrogen productivity in bioreactor studies under nongrowing conditions, where promoter-modified strains better utilized the favorable energy state created by reduced competition from cell division. Robust heterologous expression driven by the pucBa promoter is thus attractive for energy-intensive biosyntheses suited to the capabilities of R. palustris. Development of this genetic modification toolset will accelerate the advancement of R. palustris as a biotechnological chassis organism, and insights into the effects of nitrogenase overexpression will guide future efforts in engineering strains for improved hydrogen production.

Peptide-Mediated Gene Transfer into Marine Purple Photosynthetic Bacteria

Use of photosynthetic organisms is one of the sustainable ways to produce high-value products. Marine purple photosynthetic bacteria are one of the research focuses as microbial production hosts. Genetic transformation is indispensable as a biotechnology technique. However, only conjugation has been determined to be an applicable method for the transformation of marine purple photosynthetic bacteria so far. In this study, for the first time, a dual peptide-based transformation method combining cell penetrating peptide (CPP), cationic peptide and Tat-derived peptide (dTat-Sar-EED) (containing D-amino acids of Tat and endosomal escape domain (EED) connected by sarcosine linkers) successfully delivered plasmid DNA into Rhodovulum sulfidophilum, a marine purple photosynthetic bacterium. The plasmid delivery efficiency was greatly improved by dTat-Sar-EED. The concentrations of dTat-Sar-EED, cell growth stage and recovery duration affected the efficiency of plasmid DNA delivery. The delivery was inhibited at 4 °C and by A22, which is an inhibitor of the actin homolog MreB. This suggests that the plasmid DNA delivery occurred via MreB-mediated energy dependent process. Additionally, this peptide-mediated delivery method was also applicable for E. coli cells. Thus, a wide range of bacteria could be genetically transformed by using this novel peptide-based transformation method.

Method for the facile transformation of marine purple photosynthetic bacteria using chemically competent cells

Marine purple photosynthetic bacteria are ideal organisms for the production of useful materials at reduced costs and contributing to a sustainable society because they can utilize sunlight, seawater, and components of air, including carbon dioxide and nitrogen gases, for their growth. However, conjugation is the only applicable method for the transformation of marine purple photosynthetic bacteria so far. Here, we examined a calcium chloride‐mediated method for the transformation of marine purple photosynthetic bacteria. Plasmid DNAs containing the kanamycin resistance gene were successfully transferred into chemically competent cells of two strains of marine purple photosynthetic bacteria (Rhodovulum sulfidophilum and Roseospira marina). Heat shock treatment increased the transformation efficiency in R. sulfidophilum, whereas the addition of cell‐penetrating peptide did not improve it. We also found that prolonged incubation in agar plates containing kanamycin led to spontaneous mutation of the 16S rRNA, resulting in kanamycin resistance in R. marina. Thus, we developed an efficient and facile transformation method using chemically competent cells of marine purple photosynthetic bacteria with calcium chloride.

Xylanase and cellulase systems of Clostridium sp.: an insight on molecular approaches for strain improvement

Bioethanol and biobutanol hold great promise as alternative biofuels, especially for transport sector, because they can be produced from lignocellulosic agro-industrial residues. From techno-economic point of view, the bioprocess for biofuels production should involve minimal processing steps. Consolidated bioprocessing (CBP), which combines various processing steps such as pretreatment, hydrolysis and fermentation in a single bioreactor, could be of great relevance for the production of bioethanol and biobutanol or solvents (acetone, butanol, ethanol), employing clostridia. For CBP, Clostridium holds best promise because it possesses multi-enzyme system involving cellulosome and xylanosome, which comprise several enzymes such as cellulases and xylanases. The aim of this article was to review the recent developments on enzyme systems of clostridia, especially xylanase and cellulase with an effort to analyse the information available on molecular approaches for the improvement of strains with ultimate aim to improve the efficiencies of hydrolysis and fermentation.

RNA aptamers inhibit the growth of the fish pathogen viral hemorrhagic septicemia virus (VHSV)

Viral hemorrhagic septicemia virus (VHSV) is a serious disease impacting wild and cultured fish worldwide. Hence, an effective therapeutic method against VHSV infection needs to be developed. Aptamer technology is a new and promising method for diagnostics and therapeutics. It revolves around the use of an aptamer molecule, an artificial ligand (nucleic acid or protein), which has the capacity to recognize target molecules with high affinity and specificity. Here, we aimed at selecting RNA aptamers that can specifically bind to and inhibit the growth of a strain of fish VHSV both in vitro and in vivo. Three VHSV-specific RNA aptamers (F1, F2, and C6) were selected from a pool of artificially and randomly produced oligonucleotides using systematic evolution of ligands by exponential enrichment. The three RNA aptamers showed obvious binding to VHSV in an electrophoretic mobility shift assay but not to other tested viruses. The RNA aptamers were tested for their ability to inhibit VHSV in vitro using hirame natural embryo (HINAE) cells. Cytopathic effect and plaque assays showed that all aptamers inhibited the growth of VHSV in HINAE cells. In vivo tests using RNA aptamers produced by Rhodovulum sulfidophilum showed that extracellular RNA aptamers inhibited VHSV infection in Japanese flounder. These results suggest that the RNA aptamers are a useful tool for protection against VHSV infection in Japanese flounder.

Inhibition of Hirame rhabdovirus growth by RNA aptamers

RNA aptamers are artificial nucleic acids that specifically bind to a wide variety of targets. They are an effective tool for pharmaceutical research and development of antiviral agents. Here, we describe four Hirame rhabdovirus (HIRRV)-RNA aptamers (H1, H2, H3 and H4) that we obtained from an in vitro process called the systematic evolution of ligands by exponential enrichment (SELEX). The HIRRV-RNA aptamers specifically bind to HIRRV. Hirame natural embryo (HINAE) cells treated with virus and the RNA aptamer showed a decrease in appearance of cytopathic effect when compared with control (treated only with virus). Rhodovulum sulfidophilum was transformed with genes for the RNA aptamers, and the aptamers were detected in the culture medium, indicating that they were secreted from the cells. Thus, the recombinant R. sulfidophilum might be a powerful tool for the prevention of HIRRV in aquaculture.

Artificial RNA aptamer production by the marine bacterium Rhodovulum sulfidophilum: improvement of the aptamer yield using a mutated transcriptional promoter

Noncoding small RNAs and artificial RNA aptamers are now expected to be potential candidates for RNA therapeutic agents. We previously proposed a unique method for economical production of these RNAs using the marine phototrophic bacterium Rhodovulum sulfidophilum. This bacterium does not produce any ribonucleases but does produce extracellular nucleic acids in the culture medium in nature. Using this bacterium and an engineered plasmid containing the rrn promoter for the RNA expression, we developed a method for production of the streptavidin RNA aptamer in the culture medium. However, the yield of this RNA product in the culture medium by this method was not enough for practical use. In the present paper, we improved the yield of this product by modification of the -35 region of the rrn promoter so as to escape from the Fis protein control and the use of a new vector plasmid. Using this system, the extracellular RNA aptamer of approximately 200 ng and the total RNA aptamer (both extra- and intracellular form) of about 20 μg from 1 L culture were accomplished by constitutive expression of the gene.

Genetic tools for the investigation of Roseobacter clade bacteria

BACKGROUND

The Roseobacter clade represents one of the most abundant, metabolically versatile and ecologically important bacterial groups found in marine habitats. A detailed molecular investigation of the regulatory and metabolic networks of these organisms is currently limited for many strains by missing suitable genetic tools.

RESULTS

Conjugation and electroporation methods for the efficient and stable genetic transformation of selected Roseobacter clade bacteria including Dinoroseobacter shibae, Oceanibulbus indolifex, Phaeobacter gallaeciensis, Phaeobacter inhibens, Roseobacter denitrificans and Roseobacter litoralis were tested. For this purpose an antibiotic resistance screening was performed and suitable genetic markers were selected. Based on these transformation protocols stably maintained plasmids were identified. A plasmid encoded oxygen-independent fluorescent system was established using the flavin mononucleotide-based fluorescent protein FbFP. Finally, a chromosomal gene knockout strategy was successfully employed for the inactivation of the anaerobic metabolism regulatory gene dnr from D. shibae DFL12T.

CONCLUSION

A genetic toolbox for members of the Roseobacter clade was established. This provides a solid methodical basis for the detailed elucidation of gene regulatory and metabolic networks underlying the ecological success of this group of marine bacteria.

Photosynthesis genes and their expression in Rhodobacter sphaeroides 2.4.1: a tribute to my students and associates

This minireview traces the photosynthesis genes, their structure, function and expression in Rhodobacter sphaeroides 2.4.1, as applied to our understanding of the inducible photosynthetic intracytoplasmic membrane system or ICM. This focus has represented the research interests of this laboratory from the late 1960s to the present. This opportunity has been used to highlight the contributions of students and postdoctorals to this research effort. The work described here took place in a much greater and much broader context than what can be conveyed here. The 'timeline' begins with a clear acknowledgment of the work of June Lascelles and William Sistrom, whose foresight intuitively recognized the necessity of a 'genetic' approach to the study of photosynthesis in R. sphaeroides. The 'timeline' concludes with the completed genome sequence of R. sphaeroides 2.4.1. However, it is hoped the reader will recognize this event as not just a new beginning, but also as another hallmark describing this continuum.

Overexpression of integral membrane proteins for structural studies

Determination of the structure of integral membrane proteins is a challenging task that is essential to understand how fundamental biological processes (such as photosynthesis, respiration and solute translocation) function at the atomic level. Crystallisation of membrane proteins in 3D has led to the determination of four atomic resolution structures [photosynthetic reaction centres (Allenet al. 1987; Changet al. 1991; Deisenhofer & Michel, 1989; Ermleret al. 1994); porins (Cowanet al. 1992; Schirmeret al. 1995; Weisset al. 1991); prostaglandin H2synthase (Picotet al. 1994); light harvesting complex (McDermottet al. 1995)], and crystals of membrane proteins formed in the plane of the lipid bilayer (2D crystals) have produced two more structures [bacteriorhodopsin (Hendersonet al. 1990); light harvesting complex (Kühlbrandtet al. 1994)].

Chloramphenicol acetyltransferase expression in marine Rhodobacter sp. NKPB 0021 by use of shuttle vectors containing the minimal replicon of an endogenous plasmid

A vector, pUK318, was constructed to allow the expression of foreign genes in the marine photosynthetic bacterium Rhodobacter sp. NKPB 0021. This strain has been cured of its two endogenous plasmids. pUK318 consists of a 2.3-kb PstI-BamHI restriction fragment, containing a marine Rhodobacter plasmid replication region, cloned into pUC18. This fragment was derived from plasmid pRD31, a 3.1-kb endogenous plasmid purified from the marine strain Rhodobacter sp. NKPB 043402. A kanamycin resistance gene from Tn903 was cloned into the PstI restriction site to provide antibiotic selection. pUK318 was transferred to Rhodobacter sp. NKPB 0021 by transformation, and efficiencies of 7.2 x 10(-5) were obtained. Furthermore, pUK318 was stably maintained when transformants were grown either heterotrophically or photosynthetically in the absence of antibiotics. pUK318 was used to express the Escherichia coli chloramphenicol acetyl transferase (CAT) gene in Rb. NKPB 0021. Transformants expressed a maximum CAT activity of 1.12 mmol/min/g dry cells. In addition, the DNA region essential for pUK318 replication in Rb. NKPB 0021 was localized to a 1.36-kb HincII-PstI fragment. This is the first report of a plasmid vector containing a marine Rhodobacter-specific replicon that allows stable expression of foreign genes in the absence of antibiotic selection.

Transformation of the archaebacterium Halobacterium volcanii with genomic DNA

We describe optimization of a transformation system for the halophilic archaebacterium Halobacterium volcanii. Transformation of spheroplasts in the presence of polyethylene glycol permits the uptake and expression of high-molecular-weight linear fragments of genomic DNA as well as plasmid or bacteriophage DNA. Transformations can be performed with either fresh or frozen cell preparations. Auxotrophic mutants were transformed to prototrophy with genomic DNA from wild-type cells with efficiencies of 5 x 10(4)/micrograms of DNA and frequencies of 8 x 10(-5) per regenerated spheroplast. The overall efficiency of transformation with genomic DNA implies that genetic recombination is an efficient process in H. volcanii.

Gene transfer system for Rhodopseudomonas viridis

A gene transfer system for Rhodopseudomonas viridis was established which uses conjugation with Escherichia coli S17-I as the donor and mobilizable plasmids as vectors. Initially, plasmids of the incompatibility group P1 (pRK290 and pRK404) were used. The more effective shuttle vectors between E. coli and R. viridis, pKV1 and pKVS1, were derived from plasmid pBR322 and showed the highest conjugation frequency (10(-2] thus far demonstrated in purple bacteria. It was also demonstrated that Rhizobium meliloti can be used as a donor for conjugation with R. viridis. From a genomic cosmid library of R. viridis constructed in the vector pHC79, clones that coded for subunits H (puh operon), L, M and cytochrome c (puf operon) of the photosynthetic reaction center were isolated and characterized. For linkage of the two operons on the genome, cosmids that overlapped with the operon-carrying clones were identified. The relative positions of the two operons could not be determined, but the operons must be more than 100 kilobase pairs apart. Thus, the genomic organization of the reaction center in R. viridis is different from that of Rhodobacter capsulatus, for which a distance of about 39 kilobase pairs was determined. From a spontaneous mutant of R. viridis that is resistant to the herbicide terbutryn, the puf operon was cloned in pKVS1 and transferred by conjugation into R. viridis wild-type cells. The resulting exconjugants were resistant to the herbicide, which demonstrated that the puf operon on pKVS1 constructions was functionally expressed in R. viridis.

A broad-host-range vector system for cloning and translational lacZ fusion analysis

A broad-host-range vector system for studying translational fusions was constructed. The region that retains the origin of replication, nic, mob, and rep genes of the broad-host-range plasmid RSF1010 was isolated as either an HincII or a PstI-PvuII restriction fragment. These restriction fragments were ligated to tetracycline, kanamycin, or streptomycin/spectinomycin resistance genes to generate plasmids pUI501, pUI511, pUI504, and pUI506. A functional lacZ gene lacking downstream lac operon sequences together with the lac promoter was constructed from plasmids pMC1871 and pUC18. This lacZ gene was inserted into pUI501 and pUI511 to generate plasmids pUI502, pUI503, pUI512, and pUI513. An oligodeoxynucleotide sequence that carries three unique blunt-end restriction sites was synthesized, annealed, and ligated in frame to the amino-terminal end of the lacZ gene in each of these plasmids. This multiple cloning sequence will allow translational fusions to the lacZ gene in all three reading frames. The stability of these plasmids and the expression of the lacZ gene in both Escherichia coli and Rhodobacter sphaeroides were studied.

Molecular genetics of photosynthetic membrane biosynthesis in Rhodobacter sphaeroides

Images

A method for genetic transformation of nonprotoplasted Streptococcus lactis

Plasmid transformation of whole cells of Streptococcus lactis LM0230 was demonstrated. The procedure required polyethylene glycol and incubation in hypertonic media, but did not require enzymatic cell wall digestion. Conditions were optimized, yielding 5 X 10(5) transformants per micrograms of pSA3 DNA. Variables tested for effect on transformation efficiency included molecular weight, concentration, and pH of polyethylene glycol; cell density; plating media; DNA concentration; heat shock; and incubation of cells in hypertonic buffer. DNAs transformed included pSA3, pVA856, pTV1, and c2 phi. Transformation from DNA-DNA ligation mixes, with DNA not purified through density gradients, and with previously frozen cells was also achieved. The method described here for transformation of nonprotoplasted cells of LM0230 is unique, and to date has not been applied successfully to other lactic acid bacteria.

In vitro biosynthesis and membrane association of photosynthetic reaction center subunits from Rhodopseudomonas sphaeroides

The reaction center of Rhodopseudomonas sphaeroides is an integral membrane protein complex responsible for primary photochemical charge separation in photosynthesis. We report the synthesis of two of the three subunits of the photosynthetic reaction center using a DNA-directed in vitro transcription-translation system prepared from R. sphaeroides. The in vitro-synthesized polypeptides, as resolved by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, had apparent Mrs of 24,000 and 21,000 and were shown to be synthesized in equimolar amounts. This corresponds precisely to the in vivo reaction center subunits M and L, respectively. The in vitro-synthesized polypeptides were immunoprecipitated with antibody prepared against whole native reaction centers. In addition, the identity of the in vitro-synthesized polypeptides as L and M was verified by comparing the protease digestion products of in vivo- with in vitro-synthesized reaction center subunits. Both of the in vitro-synthesized polypeptides were also found to partition with the particulate material in the transcription-translation system and to associate with added membranes.

Regions of broad-host-range plasmid RK2 involved in replication and stable maintenance in nine species of gram-negative bacteria

The replication and maintenance properties of the broad-host-range plasmid RK2 and its derivatives were examined in nine gram-negative bacterial species. Two regions of RK2, the origin of replication (oriV) and a segment that encodes for a replication protein (trfA delta kilD, designated trfA*), are sufficient for replication in all nine species tested. However, stable maintenance of this minimal replicon (less than 0.3% loss per generation under nonselection conditions) is observed only in Escherichia coli, Pseudomonas aeruginosa, Pseudomonas putida, and Azotobacter vinelandii. Maintenance of this minimal replicon is unstable in Rhizobium meliloti, Agrobacterium tumefaciens, Caulobacter crescentus, Acinetobacter calcoaceticus, and Rhodopseudomonas sphaeroides. A maintenance function has been localized to a 3.1-kilobase (kb) region of RK2 encoding three previously described functions: korA (trfB korB1 korD), incP1-(II), and korB. The 3.1-kb maintenance region can increase or decrease the stability of maintenance of RK2 derivatives dependent on the host species and the presence or absence of the RK2 origin of conjugal transfer (oriT). In the case of A. calcoaceticus, stable maintenance requires an RK2 segment that includes the promoter and the kilD (kilB1) functions of the trfA operon in addition to the 3.1-kb maintenance region. The broad-host-range maintenance requirements of plasmid RK2, therefore, are encoded by multiple functions, and the requirement for one or more of these functions varies among gram-negative bacterial species.

Efficient transformation of Erwinia carotovora subsp. carotovora and E. carotovora subsp. atroseptica

We used a modified version of the method of Hanahan (D. Hanahan, J. Mol. Biol. 166:557-580, 1983) to transform Erwinia carotovora subsp. carotovora and E. carotovora subsp. atroseptica with the plasmids pBR322, pBR325, and pAT153. The transformation frequency ranged from 1 X 10(2) to 4 X 10(4) colonies per micrograms of plasmid DNA. The nature of these transformants was confirmed by plasmid analysis. ColE1-based plasmids make potentially useful cloning vectors for the study of genes involved in the pathogenesis of this species.

Induction of the photosynthetic membranes of Rhodopseudomonas sphaeroides: biochemical and morphological studies

Cells of Rhodopseudomonas sphaeroides grown in a 25% O2 atmosphere were rapidly subjected to total anaerobiosis in the presence of light to study the progression of events associated with the de novo synthesis of the inducible intracytoplasmic membrane (ICM). This abrupt change in physiological conditions resulted in the immediate cessation of cell growth and whole cell protein, DNA, and phospholipid accumulation. Detectable cell growth and whole cell protein accumulation resumed ca. 12 h later. Bulk phospholipid accumulation paralleled cell growth, but the synthesis of individual phospholipid species during the adaptation period suggested the existence of a specific regulatory site in phospholipid synthesis at the level of the phosphatidylethanolamine methyltransferase system. Freeze-fracture electron microscopy showed that aerobic cells contain small indentations within the cell membrane that appear to be converted into discrete ICM invaginations within 1 h after the imposition of anaerobiosis. Microscopic examination also revealed a series of morphological changes in ICM structure and organization during the lag period before the initiation of photosynthetic growth. Bacteriochlorophyll synthesis and the formation of the two light-harvesting bacteriochlorophyll-protein complexes of R. sphaeroides (B800-850 and B875) occurred coordinately within 2 h after the shift to anaerobic conditions. Using antibodies prepared against various ICM-specific polypeptides, the synthesis of reaction center proteins and the polypeptides associated with the B800-850 complex was monitored. The reaction center H polypeptide was immunochemically detected at low levels in the cell membrane of aerobic cells, which contained no detectable ICM or bacteriochlorophyll. The results are discussed in terms of the oxygen-dependent regulation of gene expression in R. sphaeroides and the possible role of the reaction center H polypeptide and the cell membrane indentations in the site-specific assembly of ICM pigment-protein complexes during the de novo synthesis of the ICM.

Plasmid rearrangements in the photosynthetic bacterium Rhodopseudomonas sphaeroides

Mu d1(Ap lac) was introduced into the photosynthetic bacterium Rhodopseudomonas sphaeroides 2.4.1. via the R-plasmid R751 in an attempt to isolate fusion derivatives involving photosynthetic operons. The selection system is potentially very powerful since R. sphaeroides is normally Lac negative. Among the exconjugants, photosynthesis-deficient mutants were recovered, some of which had elevated beta-galactosidase levels. Among the mutants examined, beta-galactosidase expression was linked exclusively to R751 . Many of the photosynthesis-deficient mutants were found to have alterations in their indigenous plasmids which apparently involved the exchange of DNA from one plasmid to another. Southern blot analysis revealed that there are extensive DNA sequences which are shared by the two plasmids that are involved in the rearrangements and that no exogenous DNA sequences appear to be involved. It was further discovered that plasmid rearrangement is a general phenomenon which can occur spontaneously in R. sphaeroides 2.4.1 and shows a high correlation with a photosynthesis minus phenotype.

Genetic transformation of Bacillus brevis 47, a protein-secreting bacterium, by plasmid DNA

A method has been developed for introducing plasmid DNA into Bacillus brevis 47, a protein-secreting bacterium. Treatment of B. brevis 47 cells with 50 mM Tris-hydrochloride buffer of alkaline pH was effective for inducing DNA uptake competence. In the presence of polyethylene glycol, the Tris-treated cells incorporated plasmid DNA with a frequency of 10(-4) (transformants per viable cell) when 1 microgram of plasmid DNA was added to 10(9) Tris-treated cells. The pH of Tris-hydrochloride buffer as well as the concentration and molecular weight of the polyethylene glycol affected the transformation frequency. The growth phase of B. brevis 47 cells strongly influenced the frequency. Two plasmids, pHW1 and pUB110, have been introduced into B. brevis 47 by this method. The mechanism of induction of competence for DNA uptake in connection with removal of the outer two protein layers of the cell wall by treatment of B. brevis 47 cells with Tris-hydrochloride buffer is discussed.

Identification of nitrogenase and carboxylase genes in the photosynthetic bacteria and cloning of a carboxylase gene from Rhodopseudomonas sphaeroides

The presumptive genes for the ribulose 1,5-bisphosphate carboxylase large subunit and for nitrogenase-specific components from Rhodopseudomonas sphaeroides and several other photosynthetic bacteria were identified and located by interspecific probing. Restriction digests of R. sphaeroides genomic DNA were hybridized under stringent conditions to cloned DNA from Rhodospirillum rubrum (plasmid pRR2119 carrying the carboxylase gene) and Klebsiella pneumoniae (pSA30 carrying the nitrogenase genes). The nitrogenase probe hybridized with different signal intensities to several distinct HindIII, BglII, EcoRI, BamHI and PvuII fragments of R. sphaeroides 2.4.1.DNA. The carboxylase probe hybridized to only single R. sphaeroides 2.4.1.DNA fragments produced with all five restriction enzymes. A 3000-bp EcoRI-BamHI R. sphaeroides 2.4.1.DNA fragment carrying the presumptive gene for the large subunit of ribulose 1,5-bisphosphate carboxylase was cloned into pBR322 and positively identified by probing with a 32P-labeled internal PstI fragment of the Rhodospirillum carboxylase gene.

Alterations in the phospholipid composition of Rhodopseudomonas sphaeroides and other bacteria induced by Tris

Alterations in the phospholipid head group composition of most strains of Rhodopseudomonas sphaeroides, as well as Rhodopseudomonas capsulata and Paracoccus denitrificans, occurred when cells were grown in medium supplemented with Tris. Growth of R. sphaeroides M29-5 in Tris-supplemented medium resulted in the accumulation of N-acylphosphatidylserine (NAPS) to as much as 40% of the total whole-cell phospholipid, whereas NAPS represented approximately 28 an 33% of the total phospholipid when R. capsulata and P. denitrificans respectively, were grown in medium containing 20 mM Tris. The accumulation of NAPS occurred primarily at the expense of phosphatidylethanolamine in both whole cells and isolated membranes of R. sphaeroides and had no detectable effect on cell growth under either chemoheterotrophic or photoheterotrophic conditions. Yeast extract (0.1%) and Casamino Acids (1.0%) were found to be antagonistic to the Tris-induced (20 mM) alteration in the phospholipid composition of R. sphaeroides. The wild-type strains R. sphaeroides 2.4.1 and RS2 showed no alteration in their phospholipid composition when they were grown in medium supplemented with Tris. In all strains of Rhodospirillaceae tested, as well as in P. denitrificans, NAPS represented between 1.0 and 2.0% of the total phospholipid when cells were grown in the absence of Tris. [32P]orthophosphoric acid entered NAPS rapidly in strains of R. sphaeroides that do (strain M29-5) and do not (strain 2.4.1) accumulate this phospholipid in response to Tris. Our data indicate that the phospholipid head group composition of many Rhodospirillaceae strains, as well as P. denitrificans, is easily manipulated; thus, these bacteria may provide good model systems for studying the effects of these modifications on membrane structure and function in a relatively unperturbed physiological system.